Power steering apparatus



Sept. Il, 1956 s. l. MaCDUFF POWER STEERING APPARATUS 2 Sheets-Sheet 1 Filed Aug. 14, 1 955 INVENTOR. JTANLEY .Z We Dz/Ff ATTORNEY Sept. 11, 1956 s. l. MaCDUFF PowER STEERING APPARATUS 2 shets-sheet 2 Filed Aug. 14, 1953 Y INVEN TOR. STANLEY I. MAC Duff' T TOE/VE Y United States Patent C) y 2,762,231 POWER APPARATUS Stanley I. MacDutf, South Bend, I'nd., assigner to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application August 14, 1953,'seria1 No. 374,176

"'13 Claims. (c1. 74-388) This invention concerns improvements in steering gear, .and more particularly a power steering mechanism for -land vehicles. The invention is especially adapted for use with vehicles employing a steering gear of the type having an hour-glass worm `fixed to the steering shaft for Adriving cooperation with a roller vgear pivotally carried adjacent said worm and in meshing relationship therewith for rotation about a xed center.

' It is a purpose o'f the present invention 'to introduce improvements in power steering mechanisms employing .an hour-glass worm fixed to the steering shaft.

It is an 'object of 'this kinvention to combine an hour- -glass worm mounted for axial movement from a center position 'with a roller sector gear in a manner such that lthe centers of the pitch radii of the lgears normally lie in the same plane but with the center of the pitch radius of the worm gear shifta'ble into la diie'ren't plane when there is a force resisting Vrotation of the roller gear sector `'about the center of its pitch radius.

A Astil-l further object of the invention resides in the provision of an axially displaceable hour-glass worm gear constructed and arranged to mesh closely with a roller Asector gear when the latter .is at the throat of said worm Agear and to t loosely therewith when the roller gear sector is in mesh with said worm at either side of said throat whereby axial displacement of said worm may `take place without interference between said gears.

VThe above and other objects and features of lthe invention will be apparent from ,the following description of the apparatus taken fin .connection with the accompanying drawings which fform a ,part of this 'invention and in :which: Y

Figure l is a view in longitudinal Ysection of the steering .gearot the invention associated with avchic'le; land lFigures 2, 3 and 4 represent .enlarged Vviews of the worm and sector gears in diierent positions.

VReferring now .to .Figure 1, the reference numeral designates the front wheels of a vehicle to be steered by rotation o'f a steering shaft '-12 on one end of which is mounted a wormgear 14 of the hour-.glass type. A roller sector tgear 16 .is .arranged in meshing relationship with the worm gear -and is carried byone end of a rock shaft 18, to the otherend oit-which vapitman arm 20 is secured. The rock shaftisproperly'journaled inhousing 19. The roller sector Vgear 16 is rotatably carried .on a pivot pin 22 supported at one endof the rock shaft h18. The roller sector .gear is swingable .about -the axis of the rock shaft .as .a center whichalso represents the -center of the pitch radius of vthe roller gear.V The pitman arm '20 Tisl connected to `the steering knuckle-arms V240i the wheels '10 through a steering linkage assembly Vcomprising right andle'tt reach rods `25,.a crosslinlr 28, and an idler arm 30 suitably ,pivoted at one end to Va vehicle frame 32. Thus far'the description concerns the steeringparts'involved `for conventional.manualsteering of a vehicle 'em- .ployin'gan'hour-glass worm .and rollersector gear. Except for the diierences in construction to vbe hereinafter .pointed Voutinmo`r'e detail a steering Vgearofthi's general "type employing anhor-glss Wormand ro1lerfsector"'gear iii) Patented Sept. l1, 1956 2 is known in the industry as a Marles Gear. In the standard or conventional Marles Gear the shaft on which the worm gear is mounted is held against axial displacement by thrust bearings which are located at each side of the worm, as best shown in Patents 1,642,164 and 1,720,911. It will also be observed that the roller sector gear and worm gear of Patent 1,720,911 have the same pitch radii.

This manual steering gear or Marles Gear is herein combined with a hydraulic system to provide a power steering mechanism wherein a uid motor 34 is connected between the cross link 28 and the vehicle frame 32. The uid motor 34 includes a piston 36, a piston rod 38, connected to the vehicle frame 32, and a cylinder 40 suitably attached to the cross link 28. The piston 3,6,divides the cylinder 40 into opposed chambers constantly communicating respectively with annular channels 42 and 44 of -a control Valve 45, via conduits 46 and 48. An nular channels 59, located in the interior of valve housing 52 open into a common line 54 communicating with a fluid reservoir, not shown. Annular channel 56 formed interiorly of the housing 52 communicates with an inlet conduit 58 adapted to be connected to a duid pressure source, not shown. The annular channels 42 and 44 are located in the exterior of sleeve 60 which is concentric with the steering shaft 12 and confined between ball bearing races 62. These ball bearing races abut respectively the Washer 64 and nut 66. The washer 64 is in turn in engagement with a shoulder 68 of Athe steering shaft. The nut 66 holds this entire assembly comprising parts d, 62 and 64 xed -with respect to axial movement of the steering shaft. A tubular member 7-.0 is arranged concentrically of the steering shaft v`and interposed between the latter and the sleeve 60. The sleeve cannot rotate with the steering shaft but can shift axially with the shaft. The annular channels 42 and -44 lare located between the inlet channel '56 and the annular channels 5i) and overlap the edges of channels 50 and 56 whenfthe sleeve 66 is in neutral position. In neutral ,position duid entering inlet channel 56 can ow freely .finto channels 42 `and 44 from whence the -uid passes Vinto the channels 56 communicating with Vthe reservoir, `,not gshown.

arrangement of the valve -to continuously 'circulate uid through the system results in :low pressures `throughout the system and with only light 'pump loads. Axial displacement of the sleeve 60 in either direction ffrom neutral position will increase the overlap between the inlet channel 56 and one of lthe channels 42 Vand 44 .and-decrease the Aoverlap between the inlet channel 56 and the other of the channels 42 and 44. This .axial displacement of the sleeve as aforementioned simultaneously increases the overlap Vbetween one ofthe channels 42 and 44 and one of the-channels 50 and decreases the overlap between the other of the ch'annels42and441the'otherfof the .channels This causes uid pressure :to build 'up in one `of the channels 42 vand 44 and :the end of the cylinder communicating 'with .said -one channel. The overlap between the other of the channels 42 :and 44 and one of the channels Si) -is increased, zthus providing for the free discharge of iluid :from :that vend -of .the cylinder communicating with thesaid `Vother offthechannels 42 and 44.

The sleeve 6) is yieldingly heid in its neutraljposition by a precompressed spring ,72, :arranged 'between adjacent ends or" lcoaxially disposed plungers 74.,.the51emnte ends of which abut shoulders 76 vand 78 ofthe valve housing, and the ball bearing races 62. Actually there are a plurality of plungers and springs positioned around the steering shaft but onlyy one such arrangement-is shown. The ends of the valve housing 52 areirecessed-at-Sfand 82 to freceive the rlbearing fraces 62 fwhen :the :sleeve 60 and shaft are moved-axially.V YIt is evident that any movement axially of the steering shaft must first overcome Vthe spring 772. TheV type of valve used is illustrative only,- and forms no part of the invention except as an element-bf thel combination where claimed.

One'fthe mainpoints of the inventionv resides in the construction andarrangement of the hour glass worm 14 and theroller'sector gear 16 so lthat axial displacement 'of thesteering Yshaft 12 can take place without interference'V between these gears. The Ysteering shaft 12 is rotatably supported for axial movement on radial bearings 84 located on each side of the worm 14.` For straight ahead position ofthe wheels the roller sector gear 'I6 is i normally positioned at the throat or mid position of the'worm'gear, see Figures l and 2.V In this center position of the rollerV gear, as shown in Figures l and 2, th'epitch radii S15-andV 88 of the worm and roller gears 'respectively normally lie in the same plane. The pitch radiiof the gears 14 and`16 are unequal and their pitch circles 90; and V92- aretangentl at the throat or mid position ,of the Vworrn gear. With the gears in the position 'of'Figure 2 contact pressure between the gear teeth is substantially along the pitch circles of gears. In this position of the gears vthere is a close tit between the gear teeth. However, when the rollerV sector gear is rotated in either direction from this'mid position'rthe teeth of the respective gears lit loosely, thus creating backlash between Vthe gears. This backlash permits axial displacement of the worm without interference between the gears. With reference to Figure 3 it will be observed that because the worm gear is cut to mesh with a roller sector gear having a pitch radius greater than the pitch radius 88`of the roller gear 16, rotation of the roller sector gear 16 about center C1 away from the mid position will shift the contact pressure from along the pitch circles of the gears to a point on the worm gear between the pitch circle and the addendum circle. The pitch radii of the two gears 14 and 16 are so related that during non-steering of the wheels 10 the pitch centers C1 and lCa of the pitch radii 88 and 86 are in the same plane. During steering, that is, upon rotation of steering shaft 12, the resistance offered by the wheels iti to turning is transmitted asa force to the rock shaft 13,V which reacts on the worm gear 14 to shift the center of the pitch radius of said worm gear out of said plane (see Figure 4),- to thereby shift the sleeve 60 away from its neutral position. 'Ihis axial shift of the worm becomes evident upon inspection of Figures 2, 3, and 4. In Figures 2 'and 3, the worm is substantially centrally located between the bearings 84 as represented by the distances `A and B between the wormgear and the respective bearings 84. In Figure 4, the distance B has been increased since the worm and shaft have shifted to the left as a result of the resistance Voffered to rotation ofthe sector gear about the center C2. Fluid pressure now acts in the fluid motor 34 in such a manner to cause the rock shaft to be rotated in a direction to return the center C2 to the plane containing C1 (see Figure 3), and in so doing returns the sleeve 60 to its neutral position.

*.Operation of the steering mechanism is as follows:

YAssume a condition of non-steering with the wheels 10 straight ahead. The parts of the system are in the position representedby Figures l and 2 at this time. Fluid under pressure existing in the inlet channel 56 divides equally between the channels 42 and 44, communicating with opposite ends of the cylinder 4t). From the channels 42 and 44 the uid flows into the channels 50 and thence into the common return 54. You might say that the system is'in a state of balance at this time.

Now assume a condition of steering to the right, which would be the equivalent of turning vthe wheels 16, of Figure l, clockwise about their king pin axes. In order to turn the wheels in this manner the steering shaft 12 is rotated the direction of the arrow. If the resistance to turning the wheels is greater than the resistance offered to axial displacement Yof the. shaft.Y (which is .al-Y

ways the case under normal steering conditions) the latter will be displaced to the left, see Figure 4, thus increasing the overlap between inlet channel 56 and chanV differential in pressure in the ends of cylinder`40 and.

acting on opposite sides .of` the piston 36 rotates the pitman arm 20 through link 28 in a counterclockwise direction, thus returning the worm gear and shaft to theright,l

as shown in Figure 3 to thereby provide followup. rThe sleeve 60, which had been shifted to the left', is returned tothe position of Figure l. i e i Although theinvention hasV been described in'connection with certain specific embodiments, the principles are susceptible of numerous other'applications that Ywill readily occur to persons-skilled in the art. Y

Having thusV described the'various features of the invention, what I claim as new and desire to` secure by Letters Patent is:` Y e l. In a Vpower steering mechanism, a steering shaft mounted for rotation and axial movement and having a worm gear of the hour-glass type fixedly carried thereon, said shaft having a center position from which it is shiftable in either direction, a roller sector gear arranged to mesh with said worm gear, a rock shaft on which said rollerV sector gear is'mounted for swingingV about said'rock shaft as an axis, a fluid motor, a control valve means operatively ,connectedV to said steeringrshaft andV actuable by axial movement of said shaft, and fluid connections from said valve meansv to said lluid'motor, said worm gear anderoller sector gear being so Yrelated that when the steering shaft is in center position and said roller gear sectorY is Vlocated at the throat of said worm gear the gears it closely and when the roller gear is located on either side of said throat there is substantial backlash between the gears whereby axial'movement of the steering shaft from its center position is Yeffected without interference between said gears. g

2.V A steering gear of the character dened in claim 1 wherein' the rock shaft is connected to the Vtluid motor for returning the steering shaft toward its center position after a steering application. Y Y

3. In a power steering mechanismthe combination with a worm gear of the hour-glass type mounted for limited axial movement, of a Huid m'otor, a Vvalve means controlled by axial movement of said worm and controlling the supply of uid within said motor, connections from the valve means to the uid motor, a rock shaft, and a roller gear element carried by the rock shaft and meshing with the worm, lthe gears being of such a construction and arrangement that the pitch radius of the worm gear Vis greater than the pitch radius of the roller gear element and the pitch circles are tangent when the roller gear `element is in contact with the worm gear at its throat. i 4. In a power steering mechanism the lcombination with the worm gear of the hour-glass type mounted for limited axial motion, of a uid motor, a valve means controlled by axial motion of said worm gear and` controlling the supply of fluid within said motor, connections from the valve means to the fluid motor, a rock shaft, and a roller gear carried on thegrock shaft in meshing relationship with said worm gear andhaving a mid position thereon from which Ythe roller gear is shiftable in e either direction, ,the gears Vhaving a relationship such that contact pressure between the gears is along the pitch circle of the gears Vwhen the roller gear is in saidY mid position of said worm gear and when said roller gear is out of said mid position contact pressure on the worm gear is between the pitch circle and the addendum of said last named gear thus providing backlash in all positions out of said mid position to permit axial movement of said worm gear.

5. In a power steering mechanism the combination with a Worm of the hour-glass type mounted for limited axial movement, of a fluid motor, a valve means operatively connected to said worm to respond to axial movement thereof for controlled iluid under pressure within said motor, connections from the valve means to the fluid motor, a rock shaft, and a roller gear drivably related to said worm gear and carried on the rock shaft and swngable about the axis of theV latter, the pitch radii of the pitch circles of the gears being unequal and their centers normally lying in the same plane, the pitch circles of the gears being so related that when there is a force resisting rotation of the rock shaft said center of the pitch radius of said worm gear shifts out of said plane.

6. In a power steering mechanism the combination with a rotatable steering shaft on which a worm gear of the hour-glass type is mounted for receiving a force opposing rotation of said shaft and for converting said force into axial motion of said shaft, of a uid motor, a valve means actuable by axial movement of the shaft to control fluid pressure in said motor, connections from the motor to said valve means, a rock shaft, a gear element carried by the rock shaft for engagement with said worm gear, the pitch radii of the pitch circles of the gears being unequal and With their centers normally lying in the same plane, the pitch circles of the gears being so related that when there is a force resisting rotation of the rock shaft said center of the pitch radius of said worm gear shifts out of said plane, and means operatively connecting said uid motor to said rock shaft to relieve said worm gear of the resistive force.

7. In a power steering mechanism the combination with a rotatable steering shaft on which a worm gear of the hour-glass type is mounted for receiving a force opposing rotation of said shaft and for converting said force into axial motion of said shaft, of a fluid motor, a valve means operatively connected to said shaft for actuation by the shaft upon axial movement thereof for controlling iluid pressure within said motor, connections from the valve means to said motor, a rock shaft, and a roller gear drivably related to said worm gear and supported by the rock shaft and swngable about the axis of the latter, the meshing arrangement of the gears being such that the centers of the pitch radii of the pitch circles lie in the same plane when the force resisting steering is one value and lie in diiferent planes when the force resisting steering is a second value.

8. In a steering gear, an hour-glass worm having limited axial movement in either direction from a central position, and a roller sector gear in mesh with the worm gear and arranged so that when the worm gear is held in said center position and said roller gear is positioned at the throat of said worm gear the gears mesh closely and when the roller gear is positioned on either side of the throat of said worm gear there is substantial backlash therebetween, and axial movement of said worm gear from its center position when said roller sector gear is positioned on either side of center is effected without binding between said gears.

9. In a steering gear, a roller sector gear having a given radius of operation, an hour-glass worm mounted for limited axial movement and arranged in meshing relationship to said roller sector gear, said worm being cut to mesh with a roller sector gear having a larger radius than the rollerl sector gear with which it actually meshes, the roller sector gear and worm gear being so constructed and arranged that when they are adjusted to have a closely rolling contact at the throat of the worm gear any axial movement of the latter gear will allow no more than normal full depth tooth engagement without interference when the roller sector gear is in contact with the worm gear on either side of the throat.

10. In a steering gear, an hour-glass worm mounted for limited axial displacement, a roller sector gear arranged to mesh closely with said worm when positioned at the throat of said worm and loosely with said worm when positioned on either side of the throat whereby axial displacement of the worm is effected without interference between the gears, and means for producing axial displacement of said worm.

l1. In a power steering gear, having limited axial movement in either direction from a center position, a roller gear in mesh with the worm gear and arranged with respect thereto so that when the worm gear is in said center position and said roller gear is positioned at the throat of said worm gear the gears mesh closely and when the roller gear is positioned on either side of the throat of said worm gear there is substantial backlash therebetween, manual means for producing axial movement of the worm gear away from its center position, and hydraulic power means connected to said roller gear and actuable by axial movement of said worm gear for returning said worm to its center position.

12. In a power steering mechanism, a steering shaft, radial bearings in which said shaft is rotatably mounted for axial movement, an hour-glass worm gear integrally related to said shaft, a roller sector gear arranged in meshing relationship with said worm gear and having a smaller pitch radius than the pitch radius of the worm gear, a rock shaft on which said roller sector gear is mounted for swinging about said rock shaft as an axis, a uid motor, a control valve, fluid connections between said valve and motor, said valve being connected to said steering shaft and actuable by axial movement of said worm gear and steering shaft, thereby controlling the supply of uid within said motor, said worm gear and roller sector gear having a relationship such that in the mid or throat position of the worm gear the gear teeth tit closely with the contact pressure being substantially along the pitch circles of the gears, rotation of the roller sector gear to either side of the worm throat shifting the contact pressure from along the pitch circles of the gears to a point on the worm gear between the pitch circle and the addendum circle causing the teeth of the respective gears to lit loosely, thus creating backlash between the gears which permits axial displacement of the worm without interference between the gears, said gears being arranged so that their pitch radii lie in the same plane in the throat position but in different planes when forces resisting rotation of the rock shaft cause the worm gear to shift axially.

13. In a steering gear, an hour glass worm gear, radial bearings located on each side of said worm gear and on which said worm gear is mounted for limited axial movement, a roller sector gear having a smaller pitch radius than the pitch radius of the worm gear and cut to mesh with said worm gear, said worm gear and roller sector gear being so related that when the roller sector gear is located at the throat of said worm gear the contact pressure between the gear teeth is substantially along the pitch circles of the gears, the pitch radii lie in the same plane, and the respective gears tit closely, and when the roller sector gear is located on either side of said throat the contact pressure shifts to a point on the worm gear between the pitch circle and the addendum circle, the pitch radii lie in different planes, and the respective gears t loosely, thereby creating backlash between the gears which permits axial displacement of the worm without interference between the gears.

References Cited in the le of this patent UNITED STATES PATENTS Trbojevich Sept. 13, 1932 Davis Sept. 3, 1940 an hour-glass worm 

